The present invention is generally related to a printhead for an inkjet primer and more particularly related to the design of ink feed channels for the ink firing chambers within the printhead. The present invention is related to U.S. patent application Ser. No. 08/282,670 for "Reduced Cross talk Ink Jet Printer Printhead" filed on half of Gopalan Raman on the same date herewith.
Thermal inkjet printers operate by expelling a small volume of ink through a plurality of small nozzles or orifices in a surface held in proximity to a medium upon which marks or printing is to be placed. These nozzles are arranged in a fashion in the surface such that the expulsion of a droplet of ink from a determined number of nozzles relative to a particular position of the medium results in the production of a portion of a desired character or image. Controlled repositioning of the substrate or the medium and another expulsion of ink droplets continues the production of more pixels of the desired character or image. Inks of selected colors may be coupled to individual arrangements of nozzles so that selected firing of the orifices can produce a multicolored image by the inkjet printer.
Expulsion of the ink droplet in a conventional thermal inkjet printer is a result of rapid thermal heating of the ink to a temperature which exceeds the boiling point of the ink solvent and creates a gas phase bubble of ink. Each nozzle is coupled to a small unique ink firing chamber filled with ink and having an individually addressable heating element resistor thermally coupled to the ink. As the bubble nucleates and expands, it displaces a volume of ink which is forced out of the nozzle and deposited on the medium. The bubble then collapses and the displaced volume of ink is replenished from a larger ink reservoir by way of ink feed channels.
After the deactivation of the heater resistor and the expulsion of ink from the firing chamber, ink flows back into the firing chamber to fill the volume vacated by the ink which was expelled. It is desirable to have the ink refill the chamber as quickly as possible, thereby enabling very rapid firing of the nozzles of the printhead. Rapid firing of the nozzles, of course, results in high speed printing. A large open fluid coupling between the supply of ink and the ink firing chamber would fulfill the need for high speed refilling. However, in a practical printhead where a plurality of nozzles and firing chambers exist, such a large coupling would result not only in ink being forced from the nozzle which is being fired but also being forced via the ink feed supply route to neighboring ink firing chambers and their associated nozzles. This phenomenon is commonly referred to as crosstalk, and produces imprecisely defined characters in the printed output as a result of multiple nozzles ejecting ink when only one should be doing so. Thus, some form of buffering of the common ink source is necessary to prevent crosstalk between adjacent ink firing chambers is necessary. See, for example, U.S. Pat. No. 4,882,595.
Additionally, a problem which occasionally manifests itself in inkjet printheads is that of a blockage occurring in an ink feed channel. Microscopic particles can become lodged in the narrow ink feed channel which has been used in earlier designs and starve the ink firing chamber of ink. A single nozzle which does not fire an ink droplet when it is commanded to do so will leave a missing portion out of a printed character and will leave an unprinted band on the medium when a solid image is to be printed. This results in a poorer quality of printed matter, highly undesirable for an inkjet primer. To resolve this undesirable characteristic, others have suggested using spare or redundant nozzles to eject ink in place of the defective nozzle (see U.S. Pat. No. 4,963,882 and U.S. patent application Ser. No. 08/277,723 "Kedundant Nozzle Dot Matrix Printheads and Methods of Use", filed on behalf of David E. Hackleman on Jul. 20, 1994) or multiple inlets to the ink firing chamber.
It would be desirable, therefore, to realize an inkjet printhead having improved tolerance to particle blockage and increased print speed without crosstalk between neighboring ink firing chambers and nozzles.